Dye-sensitized solar cells, developed by the Swiss researcher Michael Graetzel, are a new type of solar cell attracting attention for their high photoelectric conversion efficiency and low manufacturing cost (for example, refer to Patent Document 1 and Non-Patent Document 1).
A dye-sensitized solar cell is provided with: a working electrode having an oxide semiconductor porous film, on which a sensitizing dye made of oxide semiconductor fine particles is adsorbed, on an electrode substrate; a counter electrode that is provided so as to face this working electrode; and a electrolyte layer that is formed by an electrolyte solution being filled between the working electrode and the counter electrode.
In this type of dye-sensitized solar cell, the oxide semiconductor fine particles are sensitized by a sensitizing dye that absorbs incident light such as sunlight, with an electromotive force being generated between the working electrode and the counter electrode. Thereby, the dye-sensitized solar cell functions as a photoelectric conversion element that converts light energy into electrical power (for example, refer to Patent Document 1 and Non-Patent Document 1).
A transparent electrode substrate that is used in the above-described dye-sensitized solar cell is generally made by covering a substrate surface with a transparent conductive film of tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), or the like. However, the specific resistance of ITO or FTO is of the order of 10−4 to 10−3Ω·cm, which is a value approximately 100 times greater than the specific resistance of metal such as silver or gold. Therefore, especially when ITO or FTO is used for cells having a large surface area, this can be a cause of reducing the photoelectric conversion efficiency.
One technique of lowering the resistance of transparent electrode substrate is to increase the thickness of the transparent conductive film (such as the ITO or FTO). However, when forming the film to such a thickness that the resistance value is sufficiently lowered, the photoabsorption by the transparent conductive layer increases. For that reason, since the transmission efficiency of incident light markedly falls, a reduction in the photoelectric conversion efficiency easily occurs.
As a solution to this problem, investigations are currently underway into lowering the resistance of the electrode substrate by providing a metal wiring on the surface of the transparent electrode substrate to an extent that does not markedly impair the opening area ratio (for example, refer to Patent Document 2). In this case, in order to prevent corrosion of the metal wiring by the electrolyte solution and leak current from the metal wiring to the electrolyte solution, it is necessary for at least the surface portion of the metal wiring to be protected by a shielding layer. This shielding layer is required to cover the wiring board densely and have excellent chemical resistance to the electrolyte solution and the like that constitutes the electrolyte layer. Materials that satisfy these requirements include insulating resin, glass and the like. However, due to cases of the substrate being subjected to a thermal history such as when forming the oxide semiconductor porous film, it is preferable to use glass, which has greater heat resistance than insulating resin.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H01-220380
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2003-203681
[Non-Patent Document 1] Graetzel, M. et al, Nature, United Kingdom, 1991, vol. 353, p. 737.
However, in the case of using glass as a shielding layer, it is difficult to form a shielding layer with excellent denseness, and it is sometimes impossible to sufficiently prevent corrosion of the metal wiring by the electrolyte solution and leak current from the metal wiring to an electrolyte solution.
The present invention was made in view of the above circumstances, and has an object of providing a method of manufacturing an electrode substrate that can reliably perform shielding of a metal wiring layer and has low resistance. Also, the present invention has an object of providing a photoelectric conversion element that has an electrode substrate obtained by using the method of manufacturing an electrode substrate and is favorably used for a solar cell.